To spy on an off-duty royal for the day is a fantasy many have, including Alessandro Dell’Acqua. Backstage before his No. 21 show, he cited the most famous reigning monarch as the inspiration for his fall lineup. “Queen Elizabeth in her private life, particularly when she is gardening in the country, but in a contemporary way,” Dell’Acqua explained. The designer played with a masculine-feminine theme, and featured mannish fabrics like a heavy, almost stiff tweed, which he softened with ultrafeminine details. These looks included a tweed minidress with an organza overlay; an apronlike dress in the same fabric (“perfect for gardening,” he said) with a subtle lace hem, or a macramé top tucked into a jeweled skirt with car-wash panels. The overall effect was charming, particularly Dell’Acqua’s chunky leather gardening gloves, that came embroidered with bold cabochon stones — truly fit for a royal.